Fermentation Control

A prerequisite to a controlled fermentation is a fully hydrated, homogeneous dough, such as is obtained by correct mixing. The surface appearance of a sponge as fermentation progresses usually provides a reliable indication of the adequacy of its mixing. A properly mixed sponge will exhibit good gas retention that will make it rise and assume a well-rounded top. Retention of fermentation gasses allows loaves to develop properly and result in a light, well raised loaf after baking.

The surface of an under mixed sponge, on the other hand, will remain flat, which is indicative of an incomplete incorporation of the formula ingredients and an uneven fermentation. In straight doughs, mixing plays a much more critical role as the aim here is to obtain optimal physical dough development.

When a correctly mixed sponge or dough is fermented, two sets of forces come into play: gas production and gas retention. Gas production involves primarily the biological functioning of yeast on available fermentable carbohydrates, whereas gas retention is largely a measure of the mechanical and physicochemical modifications of the colloidal structure of the dough during mixing and during the course of fermentation.

The baker must control fermentation in such manner that the forces of gas production and gas retention are in proper balance. Thus, should gas production attain its maximum rate before the dough's gas retention capacity is fully developed, then too much gas will be lost to bring about maximum aeration of the dough. On the other hand, if the gas retention capacity has peaked before gas production has reached its maximum rate, then again much of the gas is unable to perform its aerating function. Hence, the aim of fermentation control is to have gas production capacity and gas retention capacity coincide both as to rate and time. As Clark (in Pyler) has stated, "When both peaks are reached at the same time there frequently is combined in one loaf the largest volume together with the best grain, texture, crust color, and other loaf characteristics which the flour in question will produce."

In the process of developing a bread dough, changes are brought about in the physical properties of the dough. In particular the dough's ability to retain the carbon dioxide gas, which will later be generated by yeast fermentation, is improved in the process. This improvement in gas retention ability is particularly important when the dough pieces reach the oven. In the entry stages of baking, before the dough has set, yeast activity is at its greatest level, and large quantities of carbon dioxide gas are being generated and released from solution in the aqueous phase of the dough. The dough is only able to reclaim the gas formed if a gluten structure with the correct physical structure is created. The baker must coordinate the timing of the development of the gluten structure with gas production. It does little good, for example, to develop bread with high carbon dioxide release due to proper fermentation processes, but without the degree of extensibility necessary to provide good gas retention.

Can one measure gas retention and gas production? The answer is "Yes - but" Instrumentation exists which can measure both in the same dough at the same time. It is probably not available to the vast majority of home bakers and perhaps even to most commercial bakers. It is the Chopin Rheofermentometer. This is a new instrument that simultaneously measures gas production and gas retention under realistic conditions. A piece of dough is placed in a sealed chamber under a weighted piston. As the dough rises piston movements is measured to determine the rate of expansion and the dough strength. At the same time, total gas production by yeast is measured along with the amount that escapes from the dough into the chamber. Subtracting the amount released from the total gives the amount retained. All of this is controlled by a microchip that calculates the results and produces a graph depicting "development of the Dough" and "Gaseous Release". A retention coefficient is calculated by dividing the retained volume by the total volume. (Lallemand.)

Most of the desirable changes resulting from 'optimum' dough development, whatever the breadmaking process, are related to the ability of the dough to retain gas bubbles (air) and permit the uniform expansion of the dough piece under the influence of carbon dioxide gas from yeast fermentation during proof and baking.

Gas production refers to the generation of carbon dioxide gas as a natural consequence of yeast fermentation. Provided the yeast cells in the dough remain viable (alive) and sufficient substrate (food) for the yeast is available, then gas production will continue, but expansion of the dough can only occur if that carbon dioxide gas is retained in the dough. Not all of the gas generated during the processing, proof and baking will be retained within the dough before it finally sets in the oven.

What factors effect gas production and retention? These include the following that would seem to be of interest to most home bakers.

Most flours possessing adequate baking properties pass through a stage in the course of fermentation during which gas production and gas retention are in optimum balance. The time range over which this is true may properly be designated as the flour's fermentation tolerance. Since fermentation is subject to many influences that affect its course, it is evident that one and the same flour may have rather limited fermentation tolerance under one set of conditions, and good tolerance under a different set of conditions. (See The Flour Treatise.)

Sponge Doughs

Sponge doughs generally are set to ferment at temperatures of 74 to 78F (23 to 26C), the selected temperature depending on bread making environment. It is usually more desirable to work with cool sponges and adequate levels of yeast. With approximately 2% of yeast, fermentation in a properly formulated sponge will normally proceed quite vigorously. Full maturation of the sponge will then be reached within 3 to 4.5 hr. Fermentation involves exothermic reactions that result in a temperature increase in the dough mass. The rise in sponge temperature should not exceed 10F (6C) over the entire fermentation.

In actual practice, sponge fermentation times may vary from 2.5 to 6 hr and greater. Variations of relatively wide magnitude have only a nominal effect on final bread quality as long as the minimum fermentation time exceeds 3 hr. For determining the optimum length of time required by the sponge to reach proper maturity, the so-called "drop" or "break" represents a useful point of reference. Normally, a sponge will expand to about four to five times its original size and then recede in volume. This decrease in volume, referred to as the drop or break, is quite noticeable and is taken as the point from which the additional fermentation time is calculated. Depending on whether young or old sponges are desired, the drop is taken as representing the completion of 70 to 66% of the total sponge fermentation, respectively, and the sponge is then given the additional fermentation time. Generally, well-matured flours perform better with younger sponges and in this case the post-drop time is reduced to 30%. For example, if a sponge made from a fully matured flour required 3 hr to arrive at the break, it would then be permitted to stand for an additional 54 minutes The total sponge fermentation time would thus be 3 hr and 54 minutes, or about 4 hr.

The fully fermented sponge is then returned to the mixer and mixed into the final dough which then receives additional fermentation for a relatively short time. The dough will be fully matured when it has developed shortness to a sharp pull and a rather dry feel to the touch. This stage is normally reached after a floor time of 20 to 45 min under average conditions. Warmer ambient temperatures reduce the floor time and may eliminate it altogether, while cooler temperatures tend to lengthen it.

Straight Doughs

Straight doughs are normally set at slightly higher temperatures than are sponges, i.e., within a range of 77 to 79F (25 to 26C). The accelerating effect of the higher temperatures is desirable in this case as straight doughs contain all of the dough ingredients, some of which, such as milk solids and salt, have a retarding effect on yeast action. Dough fermentation, as a rule, proceeds at a somewhat slower rate than does sponge fermentation; hence, straight doughs take longer to reach maturity than do sponges. However, the combined time of the sponge and the sponge-dough fermentations normally exceeds that of straight dough fermentation alone.

Straight doughs differ from sponges not only in their fermentation rates, but also in their handling during fermentation. The general practice is to leave sponges undisturbed until they are ready for the return to the mixer. In contrast to this, straight doughs receive periodic punching or turning, during which a good portion of the generated carbon dioxide gas is expelled, thereby reducing the dough volume.

While the actual punching or vigorous kneading of the dough is still practiced in many bakeries, the recommended procedure is to more gently turn and fold the sides of the dough well into the center. Vigorous kneading, when well-matured flours are used, has a tendency to produce bucky doughs that will subsequently create difficulties in makeup. Folding the dough, on the other hand, avoids this problem. Moreover, this method of dough manipulation assures a more uniform fermentation by equalizing the temperature throughout the dough, minimizes a possible retarding effect by excessive carbon dioxide gas accumulation within the dough, introduces atmospheric oxygen with its stimulating effect on yeast activity, and increases the gas-retaining capacity of the dough by promoting the mechanical development of its gluten through the stretching and folding action involved in this process.

This last effect appears to be of primary significance. Gas production is not constant during fermentation, but rises at first to its maximum rate and then declines. The increase in dough volume corresponds to gas production during the first hour of fermentation only. Thereafter, there is a marked decline in the rate at which dough volume increases. A dough that is permitted to go through fermentation without folding or punching will lose a considerable amount of carbon dioxide. However, if the dough is turned and folded at the right time, its gas retention properties are improved sufficiently to prevent a significant loss of gas. Under practical conditions, the rate of dough expansion is again accelerated by then folding or punch back, and this has led to the conclusion that there has been a corresponding increase in the fermentation rate. The beneficial effects of punching or folding result essentially from the improvement in the dough's gas retention properties.

The correct time at which the dough should first be turned is usually established by the simple expediency of inserting the hand into the dough, withdrawing it quickly, and observing the dough's behavior. If the dough reshapes itself, i.e., shows only a very slight recession or indentation, it is ready to be turned and folded. This point is usually taken as the 60% completion mark of the total fermentation time. The dough is then turned again after one-half this initial time, which thus represents another 30% of the total fermentation time. During the remaining 10%, the dough is sent to the divider.

The above procedure is merely indicative of general practice and must be adapted to different conditions. For example, the quality of the flour plays an important role in determining actual fermentation times. Well-matured flours normally require a shorter fermentation and less frequent punching or folding than do so-called "green" or immature flours. The fermentation time may be shortened by the simple expediency of having the first punch represent either two-thirds or even three-fourths of the total fermentation, and omitting the second punch. This procedure will yield "young" doughs. "Old" doughs, on the other hand, are obtained by having the time to the first punch represent a lesser proportion of the total fermentation. The dough will receive a series of periodic turnings or punches during this period. This practice is normally followed with strong flours of high protein content, or with lower grade flours of longer extraction. Such flours may need four or five punches; there is the risk, however, that this may give rise to bucky doughs. Slight overmixing of the doughs or increasing the absorption somewhat will ameliorate this condition. A slight increase in the dough temperature will also act to accelerate fermentation and reduce the total time.

Adjustments in Fermentation Time

Optimum fermentation time represents that point at which the effects of interacting factors such as character of flour, yeast level, temperature, formula ingredients, degree of oxidation, etc., are in balance. Once practical experience has established the most suitable procedure for processing a given type of flour, it is generally closely adhered to in the interest of uniformity. Occasions may arise, however, when it becomes necessary to either shorten or extend the established fermentation time. To meet such exigencies, certain rules have evolved concerning changes in yeast quantity and temperature that work reasonably well, but should always be regarded only as temporary expedients. This is to say that any major deviation from an accepted procedure that has yielded good results will usually result in some loss of quality. Hence, while it is possible to shorten or lengthen the fermentation time by certain adjustments in yeast and temperature, the final product will usually not meet optimum quality standards.

There is an inverse relation between the amount of yeast and fermentation time. Thus, a reduction in the amount of yeast will result in longer fermentation times, while an increase in the amount of yeast will shorten them.  A generally accepted rule is that a IF (0.5C) change in dough temperature will cause a 15 minute variation in straight-dough fermentation time. Hence, a dough that comes out of the mixer IF. warmer than normal will require about 15 minutes less fermentation under average conditions, and vice versa. Here again, practical considerations impose limits on the extent to which fermentation time may be altered; about 45 min appears to be the maximum when no other changes are involved.
 


Last Edited on: 12/25/2001 11:31:07 PM